ned said:Changes in power will also effect sound. If the voltage drops from the wall sound will change. Depending on the electrical load in your area your power company may be delivering a little less power to your house.
bandit2013 said:It looks like the arc was jumping pins 3 to 4. Caused by charge build up on the plate. Voltage spike may have originated in the output transformer due to sudden change in DC bias or load. The plates are directly coupled to the transformer, typically it should be center tapped, A/B circuit has A on one side and B on the other, one of the grids is connected close to the center tap potential probably with some windings to offset the bias. For a class A circuit, only half of the primary is used. Not sure if the B tube is operating as a dummy load or not. Arcing can ocurr across the active and or idle tube that is in parallel to it. If the holes in the socket appear clean you may be able to remove the carbon from the ceramic. Electrial parts cleaner or contact cleaner may do the trick, however, do not spray directly onto it. Spray it into a container and use a cotton rag to clean it, that stuff will damage wire insulation, eat your coverings on the amp. Not safe for most soft plastics. fine sand paper (600 grit) may help. Do not use steel wool. You may be better off replacing the socket. At least it is not connected to a PCB like the mark V. If you plan on replacing it, take many more pictures so you have reference as to what wire goes where.
bandit2013 said:The pins on tubes (unless they are gold plated) are plated with nickel. In some cases mfg may use a tin/silver or tin/copper alloy plating on the pins. If the tubes are China made, more than likely the pins are tin alloy than nickel due to ROHS initiative, as well as cost. Nickel plating is not Green or exactly ROHS compliant.
Contact cleaner will only remove carbon and organic compounds and will also disolve plastics of some types. If the pins appear shiney, cleaning is not required. If they are dark dull gray or black, contact cleaner will not clean metal oxides or sulfidation of silver terminals unless the chemical is acidic. If they are nickel, the tend to turn to dark gray due to oxidation, Silver will turn black (caused by sulfidation) and tin gray to white (caused by tin pest). Light abrasion is the only effective way to remove oxide layers. All that matters is the area that mates with the pin in the socket.
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